China may be the single biggest driver in high-voltage direct current (HVDC) power grids, but we’re still seeing the technology bridge hard-to-cross barriers in other countries as well, whether in the San Francisco Bay, or across the Red River that divides the Texas (ERCOT) and Oklahoma (SPP) power grids.

That includes the ability to transmit up to 220 megawatts of power in either direction, as well as provide “black start” support for the devilishly complex task of bringing a blacked-out grid back to an energized state, bit by bit.

Direct current lost the war to alternating current as the core technology behind the world’s modern power grids more than a century ago. But it’s still a more efficient way to move power over long distances, with about half the line losses of a comparable AC system (and close to zero line losses, if you bring superconductors into play).

ABB, for its part, built the first 200-mile, 100-kilovolt, 20-megawatt DC line in Sweden in the 1950s, and now has more than 70 projects around the world, with a total transmission capacity of more than 60,000 megawatts. Last month it announced it had tested a 1,100-kilovolt DC line, the highest voltage yet reported.

ABB also has a record for longest HVDC line, the 2,000-kilometer long, 800-kilovolt Xiangjiaba-Shanghai link, with a capacity of 6,400 megawatts. Indeed, China is by far the biggest consumer of HVDC technology. The government has said it wants to spend $269 billion through 2015 on building about 200,000 kilometers of new 330-kilovolts-and-up transmission lines -- almost the equivalent of rebuilding the United States' 257,500-kilometer transmission network from scratch. Of that, State Grid Corp. of China plans to spend a staggering $80 billion on 40,000 kilometer of ultra-high voltage (UHV) DC lines from 2011 to 2015.

Wind and solar power tends to be concentrated in under-populated areas like the High Plains and the Southwest desert in the United States, or in China’s western deserts -- not to mention the ocean. Connecting it to load centers like cities will require lots of new transmission, and HVDC offers significant advantages. (On the AC side, ABB has tackled Texas wind power with a $50 million contract to supply Electric Transmission Texas LLC with four static VAR compensators (SVCs) that will help it convert Texas’ grid to a more localized power trading system.)

That project recently raised $12 million from Japan’s Mitsui & Co., which is also working with a host of Japanese partners on projects to help Japan deal with its post-Fukushima power shortage. One big restraint is Japan’s separate northern and southern grids, which run on different frequencies. These are linked in an HVDC installation first turned on in 1965, and upgraded since then -- but today’s technology could offer increased grid-balancing features that may make it worth another upgrade.